I want to know how can one update a label present inside a GridView without having the entire GridView refresh? I am a beginner so please include some code in your explanation as well. Some one told me i need Jquery and Json, i have no idea how to use those.

Yes you can update using Jquery, which is complex to implement but a recommendable solution.
But also you can put that label inside update panel and have a timer control to refresh the label in a certain interval.